Re: [RESEND PATCH net] tap: convert a mutex to a spinlock

[David Miller]

From: Cong Wang 
Date: Mon, 10 Jul 2017 10:05:50 -0700

> We are not allowed to block on the RCU reader side, so can't
> just hold the mutex as before. As a quick fix, convert it to
> a spinlock.
> 
> Fixes: d9f1f61c0801 ("tap: Extending tap device create/destroy APIs")
> Reported-by: Christian Borntraeger 
> Tested-by: Christian Borntraeger 
> Cc: Sainath Grandhi 
> Signed-off-by: Cong Wang 

Applied and queued up for -stable, thanks.

[RESEND PATCH net] tap: convert a mutex to a spinlock

[Cong Wang]

We are not allowed to block on the RCU reader side, so can't
just hold the mutex as before. As a quick fix, convert it to
a spinlock.

Fixes: d9f1f61c0801 ("tap: Extending tap device create/destroy APIs")
Reported-by: Christian Borntraeger 
Tested-by: Christian Borntraeger 
Cc: Sainath Grandhi 
Signed-off-by: Cong Wang 
---
 drivers/net/tap.c | 18 +-
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index 9af3239..3570c75 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -106,7 +106,7 @@ struct major_info {
struct rcu_head rcu;
dev_t major;
struct idr minor_idr;
-   struct mutex minor_lock;
+   spinlock_t minor_lock;
const char *device_name;
struct list_head next;
 };
@@ -416,15 +416,15 @@ int tap_get_minor(dev_t major, struct tap_dev *tap)
goto unlock;
}
 
-   mutex_lock(_major->minor_lock);
-   retval = idr_alloc(_major->minor_idr, tap, 1, TAP_NUM_DEVS, 
GFP_KERNEL);
+   spin_lock(_major->minor_lock);
+   retval = idr_alloc(_major->minor_idr, tap, 1, TAP_NUM_DEVS, 
GFP_ATOMIC);
if (retval >= 0) {
tap->minor = retval;
} else if (retval == -ENOSPC) {
netdev_err(tap->dev, "Too many tap devices\n");
retval = -EINVAL;
}
-   mutex_unlock(_major->minor_lock);
+   spin_unlock(_major->minor_lock);
 
 unlock:
rcu_read_unlock();
@@ -442,12 +442,12 @@ void tap_free_minor(dev_t major, struct tap_dev *tap)
goto unlock;
}
 
-   mutex_lock(_major->minor_lock);
+   spin_lock(_major->minor_lock);
if (tap->minor) {
idr_remove(_major->minor_idr, tap->minor);
tap->minor = 0;
}
-   mutex_unlock(_major->minor_lock);
+   spin_unlock(_major->minor_lock);
 
 unlock:
rcu_read_unlock();
@@ -467,13 +467,13 @@ static struct tap_dev *dev_get_by_tap_file(int major, int 
minor)
goto unlock;
}
 
-   mutex_lock(_major->minor_lock);
+   spin_lock(_major->minor_lock);
tap = idr_find(_major->minor_idr, minor);
if (tap) {
dev = tap->dev;
dev_hold(dev);
}
-   mutex_unlock(_major->minor_lock);
+   spin_unlock(_major->minor_lock);
 
 unlock:
rcu_read_unlock();
@@ -1244,7 +1244,7 @@ static int tap_list_add(dev_t major, const char 
*device_name)
tap_major->major = MAJOR(major);
 
idr_init(_major->minor_idr);
-   mutex_init(_major->minor_lock);
+   spin_lock_init(_major->minor_lock);
 
tap_major->device_name = device_name;
 
-- 
2.5.5